Digital cameras include a two-dimensional pixel array. Each pixel includes a light sensitive elements that convert photons to an analog signal. The light sensitive elements can include photodiodes, phototransistors, photogates, hole accumulation diodes, pinned diodes, avalanche diodes, buried accumulation and transfer layer devices.
Various prior art pixels are known. The most commonly used pixels are either CCD pixels or CMOS pixels. Prior art CMOS pixels and two dimensional CMOS arrays are illustrated in the following U.S. patents which are incorporated herein by reference: U.S. Pat. No. 6,777,660 of Lee, titled “CMOS active pixel reset noise reduction”; U.S. Pat. No. 6,762,401 of Lee, titled “CMOS image sensor capable of increasing fill factor and driving method thereof”; U.S. Pat. No. 6,707,495 of Harada titled “solid-state imaging device and a method of reading a signal charge in a solid-state imaging device which can reduce smear and can provide an excellent image characteristics”; U.S. Pat. No. 6,750,912 of Tennant et al., titled “Active-passive imager pixel array with small groups of pixels having short common bus lines”; U.S. Pat. No. 6,697,111 of Kozlowski et al., titled “compact low-noise active pixel sensor with progressive row reset”; U.S. Pat. No. 6,665,013 of Fossum et al., titled “active pixel sensor having intra-pixel charge transfer with analog-to-digital converter”; U.S. Pat. No. 6,587,142 of Kozlowski et al., titled “low-noise active-pixel sensor for imaging arrays with high speed row reset”; U.S. Pat. No. 6,538,245 of Kozlowski, titled “amplified CMOS transducer for single photon read-out of photodetectors”; U.S. Pat. No. 6,532,040 of Kozlowski et al., titled “low-noise active-pixel sensor for imaging arrays with high-speed row reset”; U.S. Pat. No. 5,892,540 of Kozlowski et al., titled “low noise amplifier for passive pixel CMOS imager”; U.S. Pat. No. 6,438,276 of Dhuse et al., titled “imaging system having a sensor array reset noise reduction mechanism” and U.S. Pat. No. 6,326,230 of Pain et al., titled “high speed CMOS imager with motion artifact suppression and anti-blooming”.
Each pixel provides an analog signal in response to light that interacts with the light sensitive element. Due to various reasons each pixel has to receive at least a minimal amount of photons in order to provide a reasonable analog signal. This minimal amount of photons dictates an exposure period that is inversely proportional to the light intensity. In other words, smaller amounts of light result in longer exposure periods.
Relative movement between an object and the pixel array can result from movements of the object or from movement of the camera. The latter can increase as the size of cameras, especially cameras that are integrated in mobile devices such as cellular phones, decreases. This relative movement is known as camera shake.
This relative movement can cause unwanted effects such as picture blur, especially when the exposure period is not short enough in relation to that relative movement. Typically, if during the exposure period the image moves by a distance that exceeds about a half of a pixel the acquired picture is regarded as blurred.
Various method and systems for compensating for camera shake are known in the art. They usually include altering an optical characteristic of the camera, moving a certain lens and the like.
High cost telescopes compensate for air turbulence induced image errors by a costly mechanism that includes dividing an exposure period to provide multiple snapshots that are digitally stored in large memory arrays and are added to each other in complex digital circuits that include large external memories (as multiple image, each including many pixels, has to be stored), very fast buses and complex signal processing logic. It is further noted that the transmission of high-speed signals over fast buses can result in RFI problems.
There is a need to provide an efficient method and apparatus for compensating for camera shake.